Join Date: Nov 2002
Location: SouthEastern PA
Sorry it took me this long to reply. A diode is like a one-way valve for electrical current. There are a couple types, but this is the main use, and the one I'm talking about here.
(LEDs are light-emitting diodes, so current only goes through them one way ... that's why they have to be wired in a certain way. And when the current passes through, they emit light.)
About the "door ajar diodes" ... I'm not guaranteeing this is the problem, but I'm saying that, if the problem isn't in the keyless module itself, it must be in the wiring. And, if you don't see any obvious problems with the wires itself, then maybe it's one of the specific components in the wiring system (like diodes).
So, take this with a grain of salt, but one thing I noticed on my 1989 EVTM diagram is that the door ajar switches are wired into the Keyless Entry Module and the Passive Restraint Module. There are a couple of diodes in the circuit, between the switches and the Keyless Module. I was just thinking, if the diodes failed, current might be able to pass through the Passive Restraint Module and run into the Keyless Entry Module. Which would be a reverse current flow, and I thought that might cause problems.
So, it's just a suggestion of something to check. Some voltmeters have a diode-test function built in.
My EVTM says they are in the wiring harness, "230mm (9 inches) from passive restraint module." (Which is in the trunk near the KEM.)
Also, do these Thunderbirds have a battery saver feature? My 89 doesn't. Maybe after 94 they do; I don't know.
Owner, 1990 Thunderbird SC, white w/ gray cloth